Some prior art impact-absorber devices are in the form of reversible deformation systems based on dissipation of energy by dry or viscous friction. In rail transport applications they are incorporated in the buffers and in the bodies of automatic couplings. These systems have the, drawback of a low unit energy absorption capability, around 50 kJ per unit.
Another impact-absorber device is the shield disposed on the motive power unit of a train, especially high-speed trains. The shield has a honeycomb or tube construction deforming in compression. It is a large member attached to the train and has the drawback that it does not contribute to the transmission of longitudinal forces in the chassis. Also, it protects only the driver.
The safety of train passengers in the event of a collision is currently a matter of great concern. Increasing train speeds increase the danger in the event of an accident. A recent spate of accidents has shown that improvements in signalling have not eliminated all risks of collision.
An impact-absorber device that is more effective than current devices is therefore required. This device must, on impact, bring about lengthwise collapse of the axis of the motive power unit to prevent the latter from skewing on the track. It must also be light enough to satisfy train axle load limits. It must also be compact in size, since space saving is most important in the motive power units and in the passenger cars.